Polishing head of a chemical and mechanical polishing apparatus

ABSTRACT

A polishing head of a chemical and mechanical polishing apparatus includes a retainer ring which adheres more uniformly to a polishing pad. The retainer ring surrounds and protects a wafer chucked to the polishing head. The bottom surface of the retainer ring is inclined by a predetermined angle from the outer periphery thereof towards the inner periphery thereof. A resilient fixing plate disposed against the upper surface of the inner peripheral portion of the retainer ring provides a seal between the retainer ring and the carrier. Therefore, when the retainer ring is pressed against a polishing pad and the inner peripheral portion of the retainer ring is pushed downwardly due to the resiliency of the fixing plate, the retainer ring flexes such that uniform pressure is produced between the bottom surface of the retainer ring and the polishing pad. Hence, the wafer will be polished uniformly.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a chemical and mechanical polishing apparatus. More particularly, the present invention relates to the polishing head of a chemical and mechanical polishing apparatus.

[0003] 2. Description of the Related Art

[0004] A chemical and mechanical polishing process is used to planarize the front surface or the rear surface of a semiconductor wafer in the manufacturing of an integrated circuit on the wafer. The planarizing technology associated with the chemical and mechanical polishing process is becoming more important as the degree to which semiconductor integrated circuits are integrated becomes higher and the diameters of the semiconductor wafers become larger.

[0005] The chemical and mechanical polishing (CMP) apparatus used to planarize surfaces of a wafer comprises a device for mounting and detaching a wafer cassette, a wafer moving device, a polishing device, a wafer cleaning device, and a controlling device. The polishing device, in turn, comprises a polishing head for supporting and pressing a wafer, a polishing plate to which a polishing pad is attached, a driving mechanism, a device for dressing the polishing pad, a device for cleaning a wafer chuck, and a slurry supplying device.

[0006] In the mechanical aspect of the polishing process, material is removed at the surface of the wafer at a rate that is proportional to the polishing pressure and the polishing speed. In the chemical aspect of the polishing process, material is removed by a chemical reaction between the wafer surface and the slurry. As long as the polishing load, the polishing speed, the amount of slurry supplied, the friction between the wafer surface and the polishing pad, and the polishing temperature are uniform across the wafer surface, the planarizing is carried out over a wide area on the wafer and the residual layer will exhibit a uniform thickness. However, in practice, the above-mentioned parameters and the surface state of the polishing pad vary over time. Thus, the residual layer often exhibits an irregular thickness. Furthermore, the planarizing process can produce dishing and tinning phenomena, which lower the yield of the semiconductor device manufacturing process. Therefore, the above-mentioned parameters need to be controlled precisely through experimentation and the scientific process.

[0007] In addition, under 1 μm of material is polished away in the chemical and mechanical polishing process, and 0.01 μm of surface planarizing degree is needed. Therefore, the way in which the wafer is supported is very important.

[0008] One of the problems of the conventional chemical and mechanical polishing technology is that it can produce defects which reduce the die yield and product reliability. For example, if the pressure needed polishing a particular wafer is too high, the wafer carrier ring of the CMP apparatus will become considerably bent. Accordingly, the portion of the wafer carrier ring overlying the wafer will not be flat with respect to the wafer. Consequently, the flow of slurry flow becomes so bad that the wafer is polished irregularly.

[0009] In addition, a rubber bladder of the conventional CMP apparatus can leak. Therefore, preventative maintenance must be carried out to check for such potential leakage. This maintenance requires the apparatus to be down for some period of time.

[0010] Therefore, measures have been taken to reduce the bending of the retainer ring and the leakage of the bladder of a chemical and mechanical polishing head. For instance, U.S. Pat. No. 5,944,590 discloses a polishing device which includes a retainer ring rounded along the lower outer peripheral surface thereof. The difference between the lower surface of the retainer ring and the lower surface of the semiconductor wafer is 50 μm or less. U.S. Pat. No. 5,948,204 discloses a ring assembly which is attached to a rubber bladder. The ring assembly includes a plurality of rings. The first ring is made of a soft material, and supports a backing plate attached to the wafer while the wafer is being polished. The second ring is made of a hard material, and reduces the bending of the first ring while the wafer is being polished. The second ring is attached to a wafer carrier plate for preventing the rubber bladder from leaking.

[0011] U.S. Pat. No. 5,664,988 also discloses an apparatus for polishing a semiconductor wafer, the apparatus including a wafer carrier ring and a support ring. Japanese Patent Laid-Open Publication No. Hei 8-339979 discloses a method for polishing a polished substrate retaining device and a substrate. A guide member of the polished substrate retaining device is annular, and includes a passage which extends radially therethrough.

[0012]FIG. 1 is a cross-sectional view of a conventional polishing head 10. As shown in FIG. 1, the polishing head 10 includes a housing 12, a wafer carrier 14 that is mounted to the housing 12 and includes a wafer chucking plate 13, and a wafer retainer ring 16 that is mounted to the carrier 14 and maintains the wafer W in proper position on the wafer chucking plate.

[0013] The wafer carrier 14 and the retainer ring 16 are mounted to the housing 12 so as to be movable vertically relative to the housing 12. A sealing ring 15 made of a synthetic resilient material is disposed between the wafer carrier 14 and the retainer ring 16 to establish a seal therebetween.

[0014] In the conventional polishing head 10, the wafer W is pressed against a polishing pad P by a biasing force applied to the wafer carrier 14, and the wafer W is polished while the retainer ring 16 is biased against the polishing pad P by the wafer carrier 14. Therefore, the wafer W is pressed uniformly against the polishing pad P so that the entire surface of the wafer W can be uniformly polished.

[0015] However, in the polishing head 10, the outer edge of the lower surface of the retainer ring 16 is separated from the polishing pad P by the resilient force of the seal ring 15 that is exerted on the inner peripheral portion of the retainer ring 16. As a result, the pressure at which the wafer W supported by the chucking plate 13 and the retainer ring 16 are adhered to the polishing pad P becomes irregular during rotation of the polishing head 10. Accordingly, the inner peripheral portion of the retainer ring 16 is polished by the polishing pad P to form particles, and scratches are formed on the polished surface of the wafer by these particles of the retainer ring 16. The scratches constitute damage to the polished surface of the wafer W.

[0016] Furthermore, the slurry supplied between the wafer W and the polishing pad P is not uniformly distributed over the polishing pad P because the retainer ring 16 and the wafer are pressed non-uniformly against the polishing pad P. As a result, the surface of the wafer W is not polished flat.

SUMMARY OF THE INVENTION

[0017] An object of the present invention is to solve the above-described problem of the prior art. Accordingly, it is an object of the present invention to provide a polishing head of a chemical and mechanical polishing apparatus, which includes a retainer ring that will adhere uniformly to a polishing pad even when it is deflected by the resilient force of a sealing ring during the course of polishing a wafer.

[0018] In order to achieve the above-mentioned object of the present invention, the bottom surface of the retainer ring is inclined upwardly by a predetermined angle as taken in the direction extending radially from the outer periphery of the ring towards the inner periphery thereof. The retainer ring is mounted to a carrier. The carrier is in turn connected to a housing defining air passages for guiding air into and out of the polishing head. A wafer chuck is also mounted to the carrier for chucking a wafer using suction. The retainer ring extends along the outer peripheral portion of the carrier, guides the wafer chuck as it is moved towards a polishing pad, and protects the wafer chucked by the wafer chuck.

[0019] The bottom surface of the retainer ring is inclined so that when the inner peripheral portion is pushed downwardly by a sealing ring or the like, the bottom surface will be pressed uniformly against the polishing pad.

[0020] Hence, the wafer will be polished uniformly. Moreover, the bottom surface of the retainer ring will not require polishing, thereby saving time and labor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and other objects, features and advantages of the present invention will become more apparent by referring to the following detailed description thereof made with reference to the accompanying drawings, of which:

[0022]FIG. 1 is a cross-sectional view is a conventional polishing head of a chemical and mechanical polishing apparatus;

[0023]FIG. 2 is a cross-sectional view of an embodiment of a polishing head of a chemical and mechanical polishing apparatus according to the present invention;

[0024]FIG. 3 is a perspective view of a retainer ring of the polishing head according to the present invention; and

[0025]FIG. 4 is a cross-sectional view of the retainer ring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0026] A polishing head of a chemical and mechanical polishing apparatus according to the present invention will be described in detail hereinafter with reference to the FIGS. 2-4.

[0027] Referring first to FIG. 2, the polishing head 100 of a chemical and mechanical polishing apparatus according to the present invention includes a housing 110, a carrier 120 connected to the housing 110 for supporting a wafer W that is to be polished by a polishing pad P, a wafer chuck 130 that is mounted to the carrier 120 and chucks the wafer W using suction, and a retainer ring 140 that is mounted to the carrier 120. The retainer ring 140 extends along the outer periphery of the carrier 120, contacts the polishing pad P, guides the wafer chuck 130, and protects the wafer W chucked by the wafer chuck 130.

[0028] The housing 110 has a body portion 110 a for guiding the carrier 120 so that the carrier 120 can move upwardly and downwardly, and a flange portion 110 b that extends radially from the lower end of the body portion 110 a. The carrier 120 is connected to the housing 110 at the flange portion 110 b.

[0029] The body portion 110 a of the housing 110 has a circular cross section. The housing 110 also includes a guide projection 112 integral with the body portion 110 a and extending downwardly from the central portion of the lower surface of the body portion 110 a. The body portion 110 a also has a first through-hole 114 a extending longitudinally through the axial center thereof from the upper surface to the lower surface thereof, and second and third through-holes 114 b and 114 c that extend from the upper surface of the body portion 110 a to the lower surface thereof at locations spaced radially outwardly of the first though-hole 114 a. The second and third through-holes 114 b and 114 c can be located symmetrically about the first through-hole 114 a. The first, second, and third through-holes 114 a, 114 b, and 114 c function as air passages through which compressed air is introduced to and discharged from the polishing head 100.

[0030] The guide projection 112 has a through-hole 112 a. The through-hole 112 a is contiguous with the first through-hole 114 a extending through the center of the body portion 110 a. The through-hole 112 a of the projection 112 has a diameter that is larger than that of the first through-hole 114 a of the body portion 110 a.

[0031] The flange portion 110 b of the housing 110 has a plurality of through-holes spaced from one another along the outer periphery of the flange portion 110 b. The housing 110 is connected to the carrier 120 by screws inserted into these through-holes.

[0032] The carrier 120 has a body portion 122 and a connector 124 for connecting the body portion 122 to the housing 110 so that the body portion 122 can be moved upwardly and downwardly by compressed air that is introduced and discharged through the second through-hole 114 b of the housing 110. The body portion 122 of the carrier 120 defines a first axial through-hole 122 a, a second axial through-hole 122 b, a first annular recess 126 a in the upper surface of the body portion 122 thereof, and a second annular recess 126 b in the lower surface of the body portion 122.

[0033] The first through-hole 122 a has the same diameter as that of the through-hole 112 a formed in the projection 112 of the housing 110. The second through-hole 122 b spaced radially from the first through-hole 122 a and is open to the lower surface of the body portion 122 within the second annular recess 126 b

[0034] The first annular recess 126 a is concentric with respect to the center of the body portion 122 and is spaced radially inwardly from the outer periphery of the upper surface of the body portion 122. A plurality of through-holes extend through the outer peripheral portion of the body portion 122. Screws extend through these through-holes, respectively, and into tapped holes formed in the retainer ring 140 to fix the retainer ring 140 to the carrier 120.

[0035] The second annular recess 126 b is concentric with respect to the center of the body portion 122 and is located mid-way between the center of the body portion 122 and the outer periphery of the lower surface of the body portion 122. The outer periphery of the lower surface of the body portion 122 is stepped so as to define a first outer annular surface concentric with respect to the center of the lower surface of the body portion 122, and a second annular surface extending radially inwardly from the first annular surface. the second annular surface is also concentric with respect to the center of the lower surface of the body portion 122. Furthermore, the second annular surface is wider than the first outer annular surface. The outer periphery of the lower surface of the body portion 122 also includes a third annular surface that extends at an inclination from the second annular surface to the second annular recess 126 b.

[0036] The central portion of the body portion 122 of the carrier 120 is thinner than any other portion of the body portion 122. The body portion 122 also has a plurality of tapped openings in the upper surface thereof between the central portion and the first annular recess 126 a. The tapped openings are disposed radially about the central portion of the body portion 122. The connector 124 of the carrier 120 has an outer clamp 124 a that is fixed to the bottom surface of the housing 110 by nuts and bolts, an inner clamp 124 b that is fixed to the upper surface of the carrier 120 by screws extending into the tapped openings in the upper surface thereof, and an annular resilient sheet 124 c. The annular resilient sheet 124 c is made of rubber or a synthetic resin. The annular resilient sheet 124 c has a predetermined width, and the diameter of the annular resilient sheet 124 c is larger than that of the inner clamp 124 b, and is smaller than those of the carrier 120 and the outer clamp 124 a. The outer circumferential portion of the annular resilient sheet 124 c is fixed to the housing 110 by the outer clamp 124 a, whereas the inner circumferential portion of the annular resilient sheet 124 a is fixed to the carrier 120 by the inner clamp 124 b.

[0037] More specifically, the outer clamp 124 a of the connector 124 comprises a body portion and a flange portion integral with the body portion. The inner diameter of the outer clamp 124 a is larger than the outer diameter of the inner clamp 124 b, and the outer diameter of the outer clamp 124 a is equal to the maximum diameter of the housing 110. The flange portion of the outer clamp 124 a has a plurality of through-holes that correspond to the plurality of through-holes formed in the flange 110 b of the housing 110. The outer circumferential portion of the resilient sheet 124 c is disposed between the bottom surface of the housing 110 and the outer clamp 124 a. The outer clamp 124 a is fixed to the housing 110 by nuts and bolts inserted into the corresponding through-holes in the flange portion of the outer clamp 124 a and the flange 110 b of the housing 110 so as to sandwich the outer circumferential portion of the resilient sheet 124 c therebetween.

[0038] The inner clamp 124 b of the connector 124 is disc-shaped. The radius of the inner clamp 124 b is equal to the distance from the center of the carrier 120 to the first annular recess 126 a. The inner clamp 124 b has a central through-hole of a diameter that is equal to or greater than the outer diameter of the projection 112, and a plurality of through-holes that correspond to the plurality of tapped holes in the upper surface of the body portion 122 of the carrier 120. The inner clamp 124 b is fixed to the body portion 122 by screws inserted into the corresponding through-holes in the inner clamp 124 b and the tapped holes in the upper surface of the body portion 122 of the carrier 120 so as to sandwich the inner circumferential portion of the resilient sheet 124 c therebetween.

[0039] The inner clamp 124 b also has a through-hole, corresponding to the third through-hole 114 c of the housing 110, and an elongate groove having a width that is equal to the diameter of the through-hole. The through-hole of the inner clamp 124 b is spaced radially outwardly of the center of the inner clamp 124 b, and the elongate groove extends radially in the lower surface of the inner clamp 124 b from the through-hole to a position corresponding to the second through-hole 122 b of the carrier 120. An air conduit 129 is disposed in the elongate groove. The air conduit 129 has a first end connected to the third through-hole 114 c of the housing 110 and a second end connected to an annular air cushion 128 to supply and discharge air to and from the air cushion 128.

[0040] The annular air cushion 128 is disposed in the annular recess 126 defined at the lower surface of the carrier 120. The air cushion 128 is made of a flexible synthetic resin or rubber, and has an opening therein that allows air to be introduced therein or discharged therefrom. The air cushion 128 is inflated by the pressure of compressed air that is supplied through the air conduit 129 to move the wafer chuck 130 downwardly. On the other hand, the air conduit 129 is deflated when the compressed air is discharged through the air conduit 129 to allow the wafer chuck 130 to move upwardly.

[0041] The housing 110 is connected to the carrier 120 so as to define an air chamber 120 a therebetween. Compressed air introduced through the second through-hole 114 b of the housing 110 flows into the air chamber 120 a and forces the carrier 120 downwardly relative tot he housing 100. When the compressed air is discharged through the second through-hole 114 b, a vacuum is created in the air chamber 120 a. As the result, the carrier 120 is moved upwardly towards the housing 110.

[0042] The wafer chuck 130 comprises a resilient plate 132 that can be extended and retracted by air pressure, a chucking plate 134 for supporting and chucking the wafer W, a connector 136 for fixing the resilient plate 132 to the chucking plate 134 and connecting the chucking plate 134 to the carrier 120, and a guide member 138 for guiding the connecting member 136 as the chucking plate 134 moves upwardly or downwardly.

[0043] The resilient plate 132 comprises a disc of rubber or a synthetic resin. The resilient plate also has a plurality of through-holes disposed radially outwardly of the center of the resilient plate 132 at the outer peripheral portion of the resilient plate 132.

[0044] The chucking plate 134 is also disc-shaped. A plurality of through-holes extend therethrough at locations spaced radially outwardly of the center of the chucking plate 134. Air is sucked through the through-holes to chuck the wafer W to the chucking plate 134. The chucking plate 134 also has an annular recess in the upper surface thereof. The annular recess is concentric with respect to the center of the plate 134 and is located at the outer periphery of the chucking plate 134. A plurality of screw holes are disposed in the recess.

[0045] The connector 136 comprises an annular resilient sheet 136 a (of rubber or a synthetic resin) that connects the chucking plate 134 to the carrier 120 such that an air chamber 130 a is defined between the carrier 120 and the wafer chuck 130, a first connecting ring 136 b fixing the resilient plate 132 to the chucking plate 134, a second connecting ring 136 c fixing the inner peripheral portion of the resilient sheet 136 a to the chucking plate 134, and a resilient fixing ring 136 d fixing the outer peripheral portion of the resilient sheet 136 a to the carrier 120.

[0046] The outer diameter of the first connecting ring 136 b is significantly smaller than the outer diameter of the chucking plate 134. The first connecting ring 136 b also has a plurality of through-holes that correspond to the screw holes formed in the chucking plate 134. A plurality of screw holes can be formed in the upper surface of the annular sheet 136 a in alignment with the through-holes of the first connecting ring 136 b.

[0047] The resilient plate 132 is fixed to the chucking plate 134 by the first connecting ring 136 b. First, the resilient plate 132 is disposed over the lower surface of the chucking plate 134. Subsequently, the outer peripheral portion of the chucking plate 132 is bent upwardly along the outer peripheral edge of the chucking plate 134 and then is bent again into contact with the upper surface of the chucking plate 134. Next, the first connecting ring 136 b is disposed on the outer peripheral portion of the resilient plate 132 such that the though-holes formed in the first connecting ring 136 b are aligned with the through-holes formed in the outer peripheral portion of the resilient plate 132. Finally, screws are passed through the through-holes formed in the outer peripheral portions of the first connecting ring 136 b and the resilient plate 132, and into engagement with the threads of the screw holes formed in the upper surface of the chucking plate 134 to fix the resilient plate 132 to the chucking plate 134.

[0048] The second ring 136 c of the connector 136 has an outer diameter that is smaller than the outer diameter of the first connecting ring 136 b, and an inner diameter that is smaller than the inner diameter of the first connecting ring 136 b. The inner peripheral surface of the second connecting ring 136 c is machined so that it is inclined at a predetermined angle from the upper end thereof towards the lower end thereof. The diameter of the lower end of the inner peripheral surface of the second connecting ring 136 c is larger than the diameter of the upper end of the inner peripheral surface. The second connecting ring 136 c may also have a plurality of through-holes that correspond to the screw holes formed in the upper surface of the first connecting ring 136 b.

[0049] The fixing ring 136 d of the connector 136 is made of a resilient synthetic resin or rubber. The fixing ring 136 d has a thickness of about 1 mm. The maximum diameter of the fixing ring 136 d is significantly smaller than the diameter of the carrier 120. The fixing ring 136 d fixes the resilient sheet 136 a to the carrier 120, and seals the space between the carrier 120 and the retainer ring 140.

[0050] The resilient sheet 136 a has the same outer diameter as the resilient fixing ring 136 d. The resilient sheet 136 a may have a plurality of through-holes in the inner peripheral portion thereof that is interposed between the first connecting ring 136 b and the second connecting ring 136 c. ln this case, the resilient sheet 136 a is disposed between the first connecting ring 136 b and the second connecting ring 136 c such that the through-holes formed in the inner peripheral portion of the resilient sheet 136 a are aligned with the screw holes formed in the first connecting ring 136 b and the second connecting ring 136 c. Screws are passed through the screw holes formed in the first connecting ring 136 b and the through-holes formed in the inner peripheral portion of the resilient sheet 136 a and into engagement with the threads of the screw holes formed in the second connecting ring 136 c. Accordingly, the resilient sheet 136 a is connected to the first and second connecting rings 136 b and 136 c.

[0051] Alternatively, both surfaces of the inner peripheral portion of the resilient sheet 136 a may be coated with a binder, whereby the inner peripheral portion is bonded to the first connecting ring 136 b and the second connecting ring 136 c.

[0052] The outer peripheral portion of the resilient sheet 136 a may also be coated with the binder, whereby the outer peripheral portion is bonded to the lower surface of the carrier 120 and the fixing ring 136 d.

[0053] The guide member 138 comprises a disc-shaped member having a stepped portion at the outer periphery thereof, and an extending portion that extends upwardly from the center of the guide member 138. The guide member 138 has a through-hole that extends from the upper end of the extending portion to the lower surface of the guide member 138. The outer diameter of the extending portion of the guide member 138 is equal to or smaller than the inner diameter of the projection 112 of the housing 110 and the through-hole formed at the center of the carrier 120.

[0054] As shown in FIG. 2, the extending portion of the guide member 138 extends through the through-hole formed at the central portion of the carrier 120 and into the through-hole formed in the projection 112 of the housing 110. The inclined inner peripheral surface of the second connecting ring 136 c of the wafer chuck 130 is seated against the stepped portion of the guide member 138 such that the second connecting ring 136 c can slide along the stepped portion and move upwardly or downwardly according to the pressure in chamber 130 a. The upper surface of the guide member 138 is adhered to the lower surface of the carrier 120.

[0055] The through-hole formed in the guide member 138 communicates with the first through-hole 114 a formed in the housing 110, and with the air chamber 130 b defined by the guide member 138, the chucking plate 134, the connector 136, and the resilient plate 132. Therefore, when air is discharged from the air chamber 130 b through the through-hole formed in the guide member 138 and the first through-hole 114 a formed in the housing 110, a portion of the resilient plate 132 disposed on the lower surface of the chucking plate 134 is sucked into the through-holes formed in the chucking plate 134. Consequently, a vacuum is created between the resilient plate 132 and the wafer W, whereby the wafer W is adhered to the resilient plate 132.

[0056] On the other hand, the connecting member 136 of the wafer chuck 130 defines the air chamber 130 a together with the carrier 120 and the guide member 138. The pressure in the air chamber 130 a is raised when the air cushion 128 is inflated. As a result, the second connecting ring 136 c of the connector 136, the first connecting ring 136 b, and the chucking plate 134 are moved downwardly. Conversely, if the air cushion 128 is contracted by discharging the air therefrom, the air pressure in the air chamber 130 a is decreased. As a result, the second connecting ring 136 c, the first ring 136 b, and the chucking plate 134 are moved upwardly by a restoring force exerted by the resilient sheet 136 a of the connector 136.

[0057] Referring now to FIGS. 3 and 4, the retainer ring 140 of the polishing head 100 is made of a resin such as a polyphenylene sulfide PPS (resin). However, the retainer ring 140 can be made of an acethal resin or a polyether sulfone (PES) resin.

[0058] In general, the retainer ring 140 is made by cutting a section from a cylindrical body of PPS resin. Then, the section is shaped using a lathe. The inner diameter of the retainer ring 140 is about 200 mm, the outer diameter thereof is about 240 to 250 mm, and the width of the lower surface thereof is about 20 to 25 mm.

[0059] Furthermore, as shown in FIGS. 3 and 4, the retainer ring has a first step 142 and a second step 144 at the upper portion of the inner periphery thereof. The width and the height of the first step 142 are typically the same as the width and the thickness of the fixing ring 136 d, respectively. However, the height of the first step 142 may be smaller than the thickness of the fixing ring 136 d. The second step 144 of the retainer ring 140 is engaged with a jaw portion of the carrier 120. Therefore, the width and the height of the second step are the same as the width and the height of the jaw portion.

[0060] The lowermost surface 146 of the retainer ring 140 is machined so that it is inclined with respect to a (horizontal) plane orthogonal to the longitudinal axis of the ring by about 0.8 to 0.9 degrees, in the absence of any forces exerted on the ring. Preferably, the angle of inclination is 0.85 degrees. The inclined surface of the retainer ring 140 extends upwardly from the outer periphery of the retainer ring 140 towards the inner periphery of the retainer ring 140, when viewed from the bottom of the retainer ring 140. The lowermost surface 146 of the retainer ring thus subtends an angle 15 of about 89 degrees with respect to the vertical. The outer peripheral surface of the retainer ring 140 is 0.35 mm longer than the inner peripheral surface of the retainer ring 140.

[0061] A plurality of screw holes 148, preferably twelve screw holes 148, are formed in the outer peripheral portion of the upper surface of the retainer ring 140. The retainer ring 140 is fixed to the carrier 120 by screws extending through the through-holes of the carrier 120 and into engagement with the threads of the screw holes 148 formed in the retainer ring 140.

[0062] On the other hand, twelve holes (not shown) are formed between the screw holes 148 in the outer periphery of the retainer ring 140. Three holes (not shown) are formed in the inner periphery of the retainer ring 140 between each adjacent pair of screw holes 148, so that a total of thirty-six holes are formed in the inner periphery of the retainer ring 148. Each hole in the outer periphery of the retainer ring 140 communicates with a respective set of three holes in the inner periphery of the retainer ring 140. Slurry is supplied by a slurry supplying device to the holes in the outer periphery of the retainer ring 140 so that the slurry flows to the inner periphery of the retainer ring 140 through the holes in the inner periphery of the retainer ring 140. The slurry is used to polish the wafer W.

[0063] Next, the operation of the polishing head 100 according to the present invention will be described in detail.

[0064] Referring again to FIG. 2, air is discharged from the air chamber 120 a through the second through-hole 114 b of the housing 110 to vacuum the air chamber 120 a. Accordingly, a vacuum is created in the air chamber 120 a and as a result, the carrier 120 is adhered to the lower surface of the housing 110.

[0065] With the carrier 120 adhered to the lower surface of the housing 110, the retainer ring 140 and the wafer chuck 130 are disposed in an upper position. Then, air is supplied into the air cushion 128 through the air conduit 129 extending through the inner clamp 124 b and the third through hole 114 c of the housing 110. As the air cushion 128 is thus inflated, pressure is produced in the air chamber 130 a defined by the carrier body 122 of the carrier 120, the guide member 138 of the wafer chuck 130 and the connector 136. The wafer chuck 130 is moved downwardly by the air pressure produced the air chamber 130 a. More specifically, the inclined surface of the second connecting ring 136 slides along the stepped portion of the guide member 138, and the resilient plate 132 is moved downwardly until the lower surface thereof becomes coplanar with the bottom surface 146 of the retainer ring 140. Thus, the wafer chuck 130 is pressed against a wafer W fed to a location below the polishing head 100 by a wafer feeding device (not shown).

[0066] In the state in which the wafer chuck 130 is adhered to the wafer, air is discharged from the air chamber 130 b defined by the guide member 138, the chucking plate 134, and the connecting member 136 through the air passage of the extending portion of the guide member 138 and the first through-hole 114 a formed in the housing 110. Consequently, a vacuum is produced in the air chamber 130 b, and the resilient plate 132 is sucked into the through-holes formed in the chucking plate 134. Therefore, a vacuum is also produced between the chucking plate 134 and the wafer W such that the wafer W is firmly adhered to the chucking plate 134.

[0067] Subsequently, the air is discharged from the air cushion 128 to deflate the air cushion 128. Therefore, the pressure in the air chamber 130 a is lowered. Accordingly, the chucking plate 134 is moved upwardly by the resilient sheet 136 a of the connector 136. Thus, the wafer W adhered to the chucking plate 134 is positioned above the bottom surface 146 of the retainer ring 140.

[0068] Next, air is supplied into the air chamber 120 a while a vacuum is maintained in the air chamber 130 b. As a result, the body portion 122 of the carrier 120 is moved downwardly by the pressure produced in the air chamber 120 a. The retainer ring 140 and the wafer chuck 130 connected to the carrier 120 are also moved downwardly together with the carrier 120. As shown in FIG. 2, the retainer ring 140 makes contact with the upper surface of the polishing pad P. As this happens, the inner peripheral portion of the retainer ring 140 is moved downwardly by the resilient force of the fixing ring 136 d such that the retainer ring 140 contacts the upper surface of the polishing pad P uniformly. In this state, the wafer W is spaced above the upper surface of the polishing pad P.

[0069] However, the air continues to be supplied into the air chamber 120 a. Thus, the retainer ring 140 remains in contact with the upper surface of the polishing pad P. In addition, a vacuum is maintained in the air chamber 130 b. Then, air is supplied into the air cushion 128. As the air cushion 128 is thus inflated, the pressure in the air chamber 130 a is increased. As a result, the wafer chuck 130 is moved downwardly. Hence, the lower surface of the wafer W chucked by the wafer chuck 130 is brought into contact with the upper surface of the polishing pad P. The pressure in the air chamber 130 a is increased until the wafer W is adhered firmly to the polishing pad P.

[0070] In this state, the slurry is supplied between the wafer W and the polishing pad P and the polishing head 100 are rotated in opposite directions. Accordingly, the lower surface of the wafer W is polished.

[0071] Because the bottom surface of the retainer ring 140 is inclined as described above, the bottom surface of the retainer ring is pressed uniformly against the polishing pad even though the fixing ring 136 d exerts a downward force on the inner peripheral portion of the retainer ring 140.

[0072] Therefore, the retainer ring does not have to be polished. In addition, the retainer ring and the wafer are pressed uniformly against the polishing pad, thereby ensuring that the lower surface of the wafer is polished uniformly.

[0073] Finally, although the present invention has been shown and described with respect to the preferred embodiments thereof, various changes thereto and modifications thereof will become readily apparent to those of ordinary skill in the art. Accordingly, all such changes and modifications are sen to be within the true spirit and scope of the present invention as hereinafter claimed. 

What is claimed is:
 1. A polishing head of a chemical and mechanical polishing apparatus comprising: a housing defining at least one air passage therein and through which air is introduced into and discharged from the polishing head; a carrier connected to said housing so as to be movable up and down relative to said housing; a wafer chuck mounted to said carrier and communicating with a said air passage defined in the housing so that a wafer can be chucked thereto by a vacuum created when air is discharged through said air passage; a flexible retainer ring mounted to said carrier, and extending along an outer peripheral portion of the carrier around said wafer chuck so as to guide the wafer chuck and protect a wafer chucked by the wafer chuck, the retainer ring having a lowermost surface that extends upwardly at a predetermined inclination relative to the horizontal from the outer periphery thereof towards the inner periphery thereof, in the absence of forces exerted on the retainer ring; and a resilient member disposed in the polishing head so as to exert a downward force that causes the inner peripheral portion of said retainer ring to be pushed downwardly when the retainer ring is pressed downwardly against a polishing pad, whereby the retainer ring will flex to allow the lowermost surface of the retainer ring to be pressed uniformly against the polishing pad.
 2. A polishing head according to claim 1 , wherein an air chamber is defined by and between said wafer chuck and said carrier, and said resilient member is a fixing ring interposed between an upper surface of the retainer ring, at the inner peripheral portion thereof, and a lower surface of the carrier so as to seal the air chamber defined between the wafer chuck and the carrier.
 3. A polishing head according to claim 1 , wherein the lowermost surface of said retainer ring is inclined at an angle of 0.8 to 0.9 degrees relative to the horizontal.
 4. A polishing head according to claim 1 , wherein said retainer ring is made of a material selected from the group consisting of acethal resin, a polyphenylene sulfide resin, and a polyether sulfone (PES) resin.
 5. A polishing head of a chemical and mechanical polishing apparatus comprising: a housing defining a plurality of air passages therein and through which air is introduced into and discharged from the polishing head; a carrier connected to said housing so as to be movable up and down relative to said housing; a wafer chuck including a chucking plate, and a connector connecting the chucking plate to the carrier such that said chucking plate is movable upwardly and downwardly relative to said carrier; a guide member disposed between said carrier and said chucking plate, said connector defining a first air chamber together with the carrier, the chucking plate, and the guide member, said guide member and said chucking plate defining a second chamber therebetween, said guide member being engaged with said wafer chuck so as to guide said wafer chuck during up and down movement of said chucking plate, and said guide member having a through-hole that places one of said air passages defined in the housing in communication with the air chamber defined between the guide member and the chucking plate; an air cushion disposed on the lower surface of said carrier, exposed to said first air chamber and communicating with one of said air passages defined in the housing, said air cushion being inflatable and deflatable by air introduced into and discharged from the polishing head via said one of the air passages so as to change the pressure in said first air chamber and thereby selectively move said chucking plate upwardly and downwardly; a flexible retainer ring mounted to said carrier, and extending along an outer peripheral portion of the carrier around said wafer chuck so as to guide the wafer chuck and protect a wafer chucked by the wafer chuck, the retainer ring having a lowermost surface that is extends upwardly at a predetermined inclination relative to the horizontal from the outer periphery thereof towards the inner periphery thereof, in the absence of forces exerted on the retainer ring; and a resilient member disposed in the polishing head so as to exert a downward force that causes the inner peripheral portion of said retainer ring to be pushed downwardly when the retainer ring is pressed downwardly against a polishing pad, whereby the retainer ring will flex to allow the lowermost surface of the retainer ring to be pressed uniformly against the polishing pad.
 6. A polishing head according to claim 5 , wherein said resilient member is a fixing ring interposed between the inner peripheral portion of the retainer ring and a lower surface of said carrier, and sealing said first air chamber defined by said chucking plate and said carrier.
 7. A polishing head according to claim 5 , wherein the lowermost surface of said retainer ring is inclined at an angle of 0.8 to 0.9 degrees relative to the horizontal.
 8. A polishing head according to claim 5 , wherein said retainer ring is made of a material selected from the group consisting of acethal resin, a polyphenylene sulfide resin, and a polyether sulfone (PES) resin.
 9. A retainer ring for use in protecting a wafer chucked by a wafer chuck of a polishing head of a chemical mechanical polishing apparatus, said retainer ring comprising a flexible annular body having an uppermost surface, a lowermost surface, an inner peripheral surface, and an outer peripheral surface, an upper end of said inner peripheral surface adjacent the uppermost surface being stepped, a plurality of screw holes for allowing the annular body to be fixed to a carrier extending into the annular body from said uppermost surface thereof at respective locations adjacent said outer peripheral surface, and said lowermost surface being inclined upwardly at a predetermined inclination towards the uppermost surface from the outer peripheral surface of the annular body towards the inner peripheral surface thereof.
 10. A polishing head according to claim 9 , wherein the lowermost surface of said retainer ring is inclined at an angle of 0.8 to 0.9 degrees relative to a plane that extends orthogonally to the longitudinal axis of the annular body.
 11. A polishing head according to claim 9 , wherein said retainer ring is made of a material selected from the group consisting of acethal resin, a polyphenylene sulfide resin, and a polyether sulfone (PES) resin. 